1. Field of the Invention
The present invention relates generally to the design and use of medical devices, and more particularly to the design and use of an implantable port assembly for establishing extracorporeal blood circulation for hemodialysis and other blood treatments.
Access to a patient""s vascular system can be established by a variety of temporary and permanently implanted devices. Most simply, temporary access can be provided by the direct percutaneous introduction of a needle through the patient""s skin and into a blood vessel. While such a direct approach is relatively simple and suitable for certain applications, such as intravenous feeding, intravenous drug delivery, and which are limited in duration, they are not suitable for hemodialysis and other extracorporeal procedures that must be repeated periodically, often for the lifetime of the patient.
For hemodialysis and other extracorporeal treatment regimens, a variety of implantable ports have been proposed over the years. Typically, the port includes a chamber and an access region, such as a septum, where the chamber is attached to an implanted catheter which in turn is secured to a blood vessel. In the case of veins, the catheter is typically indwelling and in the case of arteries, the catheter may be attached by conventional anastomosis.
Of particular interest to the present invention, needles and other access tubes may be percutaneously attached to an implanted port in several ways. Implantable ports often include a needle-penetrable septum which permits the percutaneous penetration of a needle into the internal chamber. The chamber, in turn, is connected to one end of the implanted catheter, and the other end of the catheter is indwelling in or otherwise attached to the blood vessel. Instead of a septum, the use of needle-actuated valve mechanisms in subcutaneously implanted ports has also been proposed. See, for example, U.S. Pat. No. 5,527,278, and copending provisional application Serial No. 60/036,124, filed on Jan. 21, 1997, the latter of which is assigned to the assignee of the present invention and is incorporated herein by reference. Both the septum ports and valve ports are most commonly provided in single-port assemblies, thus requiring two separate valve ports to establish access for blood extracorporeal circulation. The use of dual-port assemblies for establishing both blood access and blood return has also been proposed. See, for example, FIGS. 3 and 4 in U.S. Pat. No. 5,527,278.
A rare but serious risk in performing hemodialysis and other extracorporeal blood circulation procedures results from accidental disconnection of the blood return needle from the implanted blood return port. Because blood is usually returned to the patient on the low pressure, venous side of the vasculature, the extracorporeal circulation system (e.g., a dialysis machine) will not necessarily be able to detect any pressure change if a venous return needle is accidentally dislodged and lost from the patient""s vein. The pressure sensed by the extracorporeal circulation system results primarily from the needle itself, so alarms built in to the circulation system are usually insufficient. Thus, since blood will continue to be drawn from the arterial side of the vasculature, the patient is at significant risk of losing large amounts of blood and even death.
For these reasons, it would be desirable to provide apparatus, systems, and methods which will reduce the risk of continued blood withdrawal during extracorporeal blood recirculation protocols in the event that the blood return needle or device becomes dislodged. In particular, it would be desirable to provide implantable port assemblies where the blood access or supply port is automatically closed in response to loss of the needle from the blood return port. Such assemblies could be in the form of dual port valve assemblies present in a single base or enclosure, or could be in the form of separately implantable single port valve assemblies where mechanical, fluid, or other coupling is provided for the interlock. The interlock provided will preferably be simple, reliable, and operate in a fail safe manner. Optionally, the port assemblies and methods may also provide for closure of the blood access port and the blood return ports on loss of the either the blood return needle or the blood access needle from the patient. At least some of the above objectives will be met by the different aspects of the present invention discussed below.
2. Description of the Background Art
Dual port vascular access assemblies are described in a number of U.S. Patents. U.S. Pat. Nos. 5,527,278; 5,527,277; 5,503,630; 5,476,451; 5,417,656; and 5,281,199, describe a dual port assembly suitable for performing hemodialysis. U.S. Pat. No. 4,108,173, describes dual port assemblies for withdrawing or introducing fluids from a single vessel. U.S. Pat. Nos. 5,399,168; 5,360,407; 5,167,638; and 4,692,146, describe dual port assemblies which are connected to blood vessels through a common lumen.
The present invention provides improved access port assemblies, apparatus, and methods which are useful for providing the simultaneous withdrawal and return of blood to a patient, usually while performing therapies requiring extracorporeal blood circulation, such as hemodialysis, hemofiltration, hemodiafiltration, apheresis, and the like. The apparatus and systems of the present invention will comprise a dual-port valve assembly or system including a first access port and a second access port. The first access port is connectable to a blood vessel or to a conduit which is connectable to a blood vessel. Similarly, the second access port is connectable to a blood vessel or to a conduit which is connectable to a blood vessel. The ports are accessible using needles or other access tubes which are percutaneously introduced and which establish a fluid connection with the blood vessel, optionally via the conduit. According to the present invention, a linkage or other interlock mechanism is provided which is coupled to the first access port and which closes the second access port in the absence of a needle or other access tube within the first access port. Thus, by relying on the first access port for blood return to the patient and the second access port for blood supply (to the extracorporeal circuit), the risk of continuing to draw blood from the second access port if the return tube is accidentally dislodged from the first access port is substantially reduced or eliminated.
In preferred aspects of the dual port valve assembly, the first linkage will also close the first access port when the return tube is absent from the first access port. In another preferred aspect, a second linkage may be provided which is coupled to the second access port and which closes both the first access port and the second access port in the absence of an access tube (in this case the blood withdrawal tube which supplies blood to the extracorporeal treatment system) in the second access port.
The dual port valve assembly will usually include all of its components within a single enclosure, referred to here and after as a xe2x80x9cbase.xe2x80x9d The components, however, may be separate in the form of a system with the first access port and second access port being separately implantable and connected by a mechanical or hydraulic linkage which is itself implanted between the two access ports. The nature of the linkage is not critical and can take virtually any form which senses the presence of an access tube within the access port and which is able to close either or both of the linked access ports whenever the access tube is removed therefrom. In a particularly preferred aspect, the linkage will be self-closing, i.e. insertion of a needle or other access tube will open the linked access port(s) against a spring or other force. When the access tube is removed, the port(s) will return to their normally closed configuration.
The first and second access ports will usually be connected to an artery as the blood supply source and a vein as the blood return, but other configurations are also possible. For example, the first and second access ports may be connected to a single blood vessel via a single, two-lumen conduit or via a pair of separate conduits. Alternatively, separate conduits may be used to connect to a vein as a blood supply source and an artery as a blood return source, although this will usually be the least preferred configuration.
In a specific embodiment of the present invention, the dual port valve assembly comprises a base having a venous passage for percutaneously receiving a venous access tube and an arterial passage for percutaneously receiving an arterial access tube. A venous conduit is disposed within the base to establish blood flow with the venous access tube which is inserted through the venous port. Similarly, an arterial conduit is disposed within the base to establish blood flow with the arterial access tube which is inserted through arterial port. A first linkage assembly is also disposed within the base and opens the arterial conduit when the venous access tube is present in the venous passage and closes the arterial conduit when the venous access tube is removed from the venous passage. Preferably, the first linkage assembly will also open the venous conduit when the venous access tube is present in the venous passage and close the venous conduit when the venous access tube is removed from the venous passage. Optionally, a second linkage assembly may be provided which opens the arterial conduit when the arterial access tube is present in the arterial passage and which closes the arterial conduit when the arterial access tube is removed from the arterial passage. Usually, the second valve assembly will also open the venous conduit when the arterial access tube is present in the arterial passage and close the venous conduit when the arterial access tube is removed from the venous passage.
Typically, the venous and arterial conduits comprise flexible, usually elastomeric, tubes and the linkage assemblies comprise clamps or xe2x80x9cpinch valvexe2x80x9d mechanisms which are spring-loaded to close the tube in the absence of an access tube in the associated access port. The flexible conduits may be adapted for direct connection to a blood vessel, may have a luer fitting or other standard connection at their distal ends, or may terminate in a fitting on the base of the valve assembly.
The present invention further provides for improved dual port valve assemblies of the type comprising a base, a first access port for receiving an access tube, a second access port for receiving an access tube, a first outlet fluidly connected to the first access port, and a second outlet fluidly coupled to the second access port, wherein the improvement comprises an interlock mechanism which prevents flow between the first access port and the first outlet when there is no access tube present in the second access port.
The present invention still further provides methods for establishing extracorporeal blood circulation for a patient""s vasculature. Such methods comprise inserting a first access tube, such as a needle, into a first subcutaneous port to withdraw blood from a blood vessel and transfer such blood into extracorporeal circulation, such as hemodialysis, hemofiltration, hemodiafiltration, apheresis, or the like. A second access tube is inserted into a second subcutaneous port to return blood from such extracorporeal circulation. The method particularly comprises terminating the withdrawal blood from the first subcutaneous port in the event that the second (return) access tube is disconnected from the second access port. Usually, the first subcutaneous access port is attached to an artery and the second subcutaneous access port is connected to a vein, but other combinations are possible as described above. The terminating step preferably comprises actuating a linkage between the first access port and the second access port, wherein the linkage usually closes a conduit which connects the blood vessel to the first subcutaneous port. Typically, insertion of the first access tube into the first subcutaneous port will also cause opening of the second access tube, usually against a spring or other stored-energy mechanism, so that subsequent removal of the access tube will result in immediate reclosing of the second access port in a xe2x80x9cfail safexe2x80x9d manner. In preferred aspects of the method, the linkage also closes conduit which connects the blood vessel to the second subcutaneous port, and the method further comprises actuating a second linkage which closes both the first and second access ports in the event that the first access tube is disconnected from the first access port.
When blood withdrawal from the first subcutaneous port terminates as a result of disconnection of the second (return) access tube from the second access port, the extracorporeal circulation system, e.g. dialysis machine, will preferably be able to monitor and detect the flow termination, typically by detecting a decrease in pressure in the first access tube which is connected to the first access port. The pressure decrease, of course, will typically result from closure of the first access port in the manner described above.